Method and system to detect P-waves in cardiac arrhythmic patterns

Abstract

Methods and systems are provided for detecting arrhythmias in cardiac activity. The methods and systems declare a current beat, from the CA signals, to be a candidate beat or an ineligible beat based on whether the current beat satisfies the rate based selection criteria. The determining and declaring operations are repeated for multiple beats to form an ensemble of candidate beats. The method and system calculate a P-wave segment ensemble from the ensemble of candidate beats, perform a morphology-based comparison between the P-wave segment ensemble and at least one of a monophasic or biphasic template, declare a valid P-wave to be present within the CA signals based on the morphology-based comparison, and utilize the valid P-wave in an arrhythmia detection process to determine at least one of an arrhythmia entry, arrhythmia presence or arrhythmia exit.

What is claimed is: 
     
       1. A computer implemented method for detecting arrhythmias in far field cardiac activity (CA) signals collected by two or more electrodes located remote from a right atrium, comprising:
 under control of one or more processors configured with specific executable instructions, 
 declaring beats, from the CA signals, that satisfy a rate based selection criteria to be candidate beats; 
 calculating a P-wave segment ensemble by combining candidate P-wave segments from the far field CA signals for the candidate beats; 
 performing a comparison between the P-wave segment ensemble and the candidate P-wave segments; 
 determining a number of eligible P-waves based on the comparison; and 
 utilizing the number of eligible P-waves in an arrhythmia detection process to determine at least one of an arrhythmia entry, arrhythmia presence, absence of an arrhythmia or arrhythmia exit. 
 
     
     
       2. The method of  claim 1 , further comprising determining the candidate beats by applying a two-part selection test that includes i) determining whether an RR interval of a candidate beat is within a predetermined range and ii) determining whether the RR interval of the candidate beat is greater or shorter than the RR interval of a previous beat, and if shorter, determining whether the candidate beat has a duration that is within a range of the previous beat. 
     
     
       3. The method of  claim 1 , further comprising:
 overlaying a P-wave search window onto a candidate segment within the corresponding candidate beats to obtain candidate P-wave segments; 
 combining the candidate P-wave segments to form a P-wave combination; and 
 determining whether a signal characteristic of interest from the P-wave combination exceeds one or more P-wave limits. 
 
     
     
       4. The method of  claim 3 , further comprising truncating one or more of the candidate P-wave segments when a signal characteristic of the corresponding candidate P-wave segment exceeds one or more P-wave limits, the calculating operation calculating a final P-wave segment ensemble based on the candidate P-wave segments after truncation. 
     
     
       5. The method of  claim 1 , further comprising de-trending the ensemble of candidate beats to remove baseline drift from individual P-wave segments for corresponding candidate beats. 
     
     
       6. The method of  claim 1 , the performing the comparison further comprising correlating a shape of a first P-wave segment, for a first beat from the candidate beats, with a shape of the P-wave segment ensemble for morphology similarity analysis. 
     
     
       7. The method of  claim 1 , wherein the determining the number of eligible P-waves further comprises:
 forming a final P-wave segment ensemble by removing the candidate P-wave segments that do not satisfy the comparison, the final P-wave segment ensemble retaining only the eligible P-waves; and 
 declaring a valid P-wave to be present within the CA signals when a correlation between the P-wave segment ensemble and a template satisfies a correlation threshold. 
 
     
     
       8. The method of  claim 1 , further comprising:
 providing an implantable cardiac monitor (ICM) having a housing that encloses the one or more processors configured with the specific executable instructions, the two or more electrodes provided on the housing and located remote from a heart; and 
 collecting the far field CA signals along a sensing vector extending between the two or more electrodes located remote from the heart. 
 
     
     
       9. The method of  claim 1 , wherein performing the comparison further comprises performing a morphology-based comparison that includes determining a level of correlation between a shape of the P-wave segment ensemble and a shape of the candidate P-wave segments. 
     
     
       10. The method of  claim 1 , further comprising forming a final P-wave segment ensemble by removing, from the P-wave segment ensemble, the candidate P-wave segments that do not satisfy the comparison, the determining including determining the eligible number of candidate P-wave segments that remain in the final P-wave segment ensemble. 
     
     
       11. A system for detecting arrhythmias in far field cardiac activity (CA) signals collected by two or more electrodes located remote from a right atrium, comprising:
 memory to store specific executable instructions; 
 one or more processors configured to execute the specific executable instructions for:
 declaring beats, from the CA signals, that satisfy a rate based selection criteria to be candidate beats; 
 calculating a P-wave segment ensemble by combining candidate P-wave segments from the far field CA signals for the candidate beats; 
 performing a comparison between the P-wave segment ensemble and the candidate P-wave segments; 
 determining a number of eligible P-waves based on the comparison; and 
 utilizing the valid P-wave in an arrhythmia detection process to determine at least one of an arrhythmia entry, arrhythmia presence, absence of an arrhythmia or arrhythmia exit. 
 
 
     
     
       12. The system of  claim 11 , wherein the one or more processors are configured to determine the candidate beats by applying a two-part selection test that includes i) determining whether an RR interval of a candidate beat is within a predetermined range and ii) determining whether the RR interval of the candidate beat is greater or shorter than the RR interval of a previous beat, and if shorter, determining whether the candidate beat has a duration that is within a range of the previous beat. 
     
     
       13. The system of  claim 11 , wherein the one or more processors are configured to further:
 overlay a P-wave search window onto a candidate segment within corresponding candidate beats to obtain candidate P-wave segments; 
 combine the candidate P-wave segments to form a P-wave combination; and 
 determine whether a signal characteristic of interest from the P-wave combination exceeds one or more P-wave limits. 
 
     
     
       14. The system of  claim 13 , wherein the one or more processors are further configured to truncate one or more of the candidate P-wave segments when a signal characteristic of the corresponding candidate P-wave segment exceeds one or more P-wave limits, the calculating operation calculating a final P-wave segment ensemble based on the candidate P-wave segments after truncation. 
     
     
       15. The system of  claim 11 , wherein the one or more processors are further configured to de-trend the ensemble of candidate beats to remove baseline drift from individual P-wave segments for corresponding candidate beats. 
     
     
       16. The system of  claim 11 , wherein, to perform the comparison, the one or more processors are further configured to correlate a shape of a first P-wave segment, for a first beat from the candidate beats, with a shape of the P-wave segment ensemble for morphology similarity analysis. 
     
     
       17. The system of  claim 11 , wherein, to determine the number of eligible P-waves, the one or more processors are further configured to:
 form a final P-wave segment ensemble by removing the candidate P-wave segments that do not satisfy the comparison, the final P-wave segment ensemble retaining only the eligible P-waves; and 
 declare a valid P-wave to be present within the CA signals when a correlation between the P-wave segment ensemble and a template satisfies a correlation threshold. 
 
     
     
       18. The system of  claim 11 , wherein the one or more processors are further configured to declare the P-wave segment ensemble to not include a P-wave when a correlation between the P-wave segment ensemble and at least one a monophasic or biphasic templates do not satisfy a correlation threshold. 
     
     
       19. The system of  claim 11 , further comprising:
 an implantable cardiac monitor (ICM) having a housing that encloses the memory and the one or more processors, the two or more electrodes provided on the housing and configured to be located remote from a heart, the two or more electrodes configured to collect the far field CA signals along a sensing vector extending between the two or more electrodes located remote from the heart. 
 
     
     
       20. The system of  claim 11 , wherein the one or more processors are further configured to perform the comparison by performing a morphology-based comparison that includes determining a level of correlation between a shape of the P-wave segment ensemble and a shape of the candidate P-wave segments. 
     
     
       21. The system of  claim 11 , wherein the one or more processors are further configured to form a final P-wave segment ensemble by removing, from the P-wave segment ensemble, the candidate P-wave segments that do not satisfy the comparison, the determining including determining the eligible number of candidate P-wave segments that remain in the final P-wave segment ensemble.